U.S. patent number 5,543,942 [Application Number 08/356,553] was granted by the patent office on 1996-08-06 for lcd microlens substrate with a lens array and a uniform material bonding member, each having a thermal resistance not lower than 150.degree.c.
This patent grant is currently assigned to Omron Corporation, Sharp Kabushiki Kaisha. Invention is credited to Shigeru Aoyama, Hiroshi Hamada, Yoshihiro Mizuguchi, Tsukasa Yamashita.
United States Patent |
5,543,942 |
Mizuguchi , et al. |
August 6, 1996 |
LCD microlens substrate with a lens array and a uniform material
bonding member, each having a thermal resistance not lower than
150.degree.C
Abstract
The present invention discloses an opposed substrate for use in
a liquid crystal display element, for example. The opposed
substrate is constructed by a transparent substrate, microlenses
formed on the substrate, a bonding layer, and cover glass. An
alignment film and transparent electrodes are formed on the cover
glass. The microlenses and the bonding layer are formed by selected
resins which have thermal resistance to high temperatures not lower
than 150.degree. C., permit heating treatment for forming the
alignment film, and satisfy the difference in the refractive
indexes between the resins, .increment.n.gtoreq.0.1, so as to
enable the microlenses to have a numerical aperture not lower than
0.1. It is thus possible to prevent the decomposition of resins and
separation of the microlens in heat treatment and to provide a
high-quality, highly reliable liquid crystal display element.
Inventors: |
Mizuguchi; Yoshihiro (Tenri,
JP), Hamada; Hiroshi (Nara, JP), Aoyama;
Shigeru (Kyoto, JP), Yamashita; Tsukasa (Nara,
JP) |
Assignee: |
Sharp Kabushiki Kaisha (Osaka,
JP)
Omron Corporation (Kyoto, JP)
|
Family
ID: |
26564803 |
Appl.
No.: |
08/356,553 |
Filed: |
December 15, 1994 |
Foreign Application Priority Data
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Dec 16, 1993 [JP] |
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5-317145 |
Dec 9, 1994 [JP] |
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6-306650 |
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Current U.S.
Class: |
349/5; 349/122;
359/619 |
Current CPC
Class: |
B29D
11/00278 (20130101); G02B 3/0031 (20130101); G02F
1/133526 (20130101); G02F 1/1333 (20130101) |
Current International
Class: |
B29D
11/00 (20060101); G02F 1/13 (20060101); G02B
3/00 (20060101); G02F 1/1335 (20060101); G02F
1/1333 (20060101); G02F 001/1335 (); G02F
001/1333 () |
Field of
Search: |
;359/40,41,81,74,619,620,626,455 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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5056912 |
October 1991 |
Hamada et al. |
5076511 |
December 1991 |
Stein et al. |
5093574 |
March 1992 |
Pratt et al. |
5185601 |
February 1993 |
Takeda et al. |
5225935 |
July 1993 |
Watanabe et al. |
5335102 |
August 1994 |
Kanemori et al. |
5381187 |
January 1995 |
Takamatsu et al. |
|
Foreign Patent Documents
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|
|
|
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|
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0426441A2 |
|
May 1991 |
|
EP |
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54-17620 |
|
Feb 1979 |
|
JP |
|
57-9180 |
|
Jan 1982 |
|
JP |
|
60-165623 |
|
Aug 1985 |
|
JP |
|
60-165624 |
|
Aug 1985 |
|
JP |
|
60-165621 |
|
Aug 1985 |
|
JP |
|
60-165622 |
|
Aug 1985 |
|
JP |
|
60-262131 |
|
Dec 1985 |
|
JP |
|
63-44624 |
|
Feb 1988 |
|
JP |
|
3-202330 |
|
Sep 1991 |
|
JP |
|
3230567 |
|
Oct 1991 |
|
JP |
|
3-233417 |
|
Oct 1991 |
|
JP |
|
3-248125 |
|
Nov 1991 |
|
JP |
|
5-88161 |
|
Apr 1993 |
|
JP |
|
5-134103 |
|
May 1993 |
|
JP |
|
5-273512 |
|
Oct 1993 |
|
JP |
|
6175120 |
|
Jun 1994 |
|
JP |
|
6232379 |
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Aug 1994 |
|
JP |
|
Other References
Distributed-Index Planar Microlens . . . , M. Oikawa et al.,
Electronics Letters, Jun. 1981, vol. 17, No. 13, pp. 452-454. .
New Fabrication Method of Plastic Micro Lens, T. Suzuki et al.,
24th Microoptics Research Paper, pp. 20-25. .
Technique for Monolithic Fabrication . . . , Z. Popovic et al.,
Applied Optics, vol. 27, No. 7, Apr. 1988, pp. 1281-1284..
|
Primary Examiner: Pellman Gross; Anita
Assistant Examiner: Ton; Toan
Claims
What is claimed is:
1. A microlens substrate comprising:
a first transparent substrate;
an array of converging members for converging incident light, said
converging members being made of a material having thermal
resistance to high temperatures not lower than 150.degree. C. and
being arranged on said first transparent substrate;
a second transparent substrate placed on said converging members;
and
a bonding member, made of a uniform material having thermal
resistance to high temperatures not lower than 150.degree. C., for
bonding said converging members and said second transparent
substrate.
2. The microlens substrate according to claim 1, wherein said
converging members are a microlens array or a lenticular lens.
3. The microlens substrate according to claim 2, wherein a
numerical aperture of said microlens array or lenticular lens is
not smaller than 0.1.
4. The microlens substrate according to claim 2, wherein the
difference .increment.n in refractive indexes between said
microlens array or lenticular lens and said bonding member is not
smaller than 0.1.
5. The microlens substrate according to claim 1, wherein said
converging members and said bonding member are formed by
ultraviolet sensitive resins.
6. A liquid crystal display element comprising an opposed substrate
including:
(a) a first transparent substrate;
(b) an array of converging members for converging incident light,
said converging members having thermal resistance to high
temperatures not lower than 150.degree. C. and being arranged on
said first transparent substrate;
(c) a second transparent substrate placed on said converging
members, and
(d) a bonding member made of a uniform material having thermal
resistance to high temperatures not lower than 150.degree. C., for
bonding said converging members and said second transparent
substrate,
wherein transparent electrodes, an alignment film, and a black
matrix are formed on said opposed substrate,
said liquid crystal display element further comprising:
an active matrix substrate; and
a liquid crystal layer formed between said opposed substrate and
said active matrix substrate.
7. The liquid crystal display element according to claim 6,
wherein said first transparent substrate, said second transparent
substrate, and said active matrix substrate are formed by the same
material.
8. The liquid crystal display element according to claim 6,
wherein said converging members and said bonding member are formed
by ultraviolet sensitive resins.
9. The liquid crystal display element according to claim 6,
wherein said converging members are a microlens array or a
lenticular lens having a numerical aperture not smaller than
0.1.
10. The liquid crystal display element according to claim 6,
wherein said converging members are a microlens array or a
lenticular lens, and
the difference .increment.n in refractive indexes between said
microlens array or lenticular lens and said bonding member is not
smaller than 0.1.
11. A liquid crystal projector using a liquid crystal display
element,
said liquid crystal display element comprising:
(1) an opposed substrate including a first transparent substrate,
an array of converging members for converging incident light, said
converging members having thermal resistance to high temperatures
not lower than 150.degree. C. and being arranged on said first
transparent substrate, a second transparent substrate placed on
said converging members, and a bonding member made of a uniform
material having thermal resistance to high temperatures not lower
than 150.degree. C., for bonding said converging members and said
second transparent substrate, wherein transparent electrodes, an
alignment film and a black matrix are formed on said opposed
substrate;
(2) an active matrix substrate; and
(3) a liquid crystal layer formed between said opposed substrate
and said active matrix substrate,
said liquid crystal projector comprising a projection lens for
projecting light transmitted through said liquid crystal display
element onto a screen,
wherein a numerical aperture of said projection lens is larger than
a numerical aperture of said converging members.
12. The liquid crystal projector according to claim 11,
wherein said converging members and said bonding member are formed
by ultraviolet sensitive resin.
13. The liquid crystal projector according to claim 11,
wherein said converging members are a microlens array or a
lenticular lens having a numerical aperture not smaller than
0.1.
14. The liquid crystal projector according to claim 11,
wherein said converging members are a microlens array or a
lenticular lens, and
the difference .increment.n in refractive indexes between said
microlens array or lenticular lens and said bonding member is not
smaller than 0.1.
15. A method for manufacturing a microlens substrate comprising the
steps of:
preparing a first transparent substrate;
forming an array of converging means, made of a material having a
thermal resistance to high temperatures not lower than 150.degree.
C. on said first transparent substrate, for converging incident
light;
preparing a second transparent substrate; and
bonding said converging means and said second transparent substrate
with a bonding member made of a uniform material having thermal
resistance to high temperatures not lower than 150.degree. C.
16. The method of claim 15, further including the subsequent step
of:
forming transparent electrodes, an alignment film, and a black
matrix on said second transparent substrate under temperatures not
lower than 150.degree. C.
17. The method of claim 15, wherein the bonding member is a single
material including photosensitive resin.
Description
FIELD OF THE INVENTION
The present invention relates to a microlens substrate having
microlenses, a high-definition liquid crystal display element using
the microlens substrate, and a liquid crystal projector using the
liquid crystal display element.
BACKGROUND OF THE INVENTION
The word "microlens" used in this specification means not only a
minute lens whose size is not larger than several millimeters, but
also a microlens array formed by one-dimensionally or
two-dimensionally aligning a plurality of such minute lenses and a
lenticular lens. In this specification, a liquid crystal projector
not only means a device having a light source, a liquid crystal
display element, image coloring means, an optical system for
enlarging and projecting an image displayed by the liquid crystal
display element onto a screen and means for driving the liquid
crystal display element, but also includes an apparatus in which
the above device and the screen are formed as a single piece.
The demand for projection-type liquid crystal display elements such
as projection televisions as well as direct-viewing liquid crystal
display elements increase. When a liquid crystal display element is
used as a projection-type display, if images are enlarged without
changing the number of pixels used in a conventional display
element, a less definite view will result. In order to obtain
highly definite images, it is necessary to increase the number of
pixels when enlarging images.
However, if the number of pixels in a liquid crystal display
element, particularly, in an active-matrix liquid crystal display
element is increased, the area occupied by the pixels becomes
relatively small while the area of a black matrix covering other
than the pixels increases. If the area of the black matrix
increases, the area of the apertures of pixels used for displaying
images is decreased and the aperture ratio of the display element
is lowered. When the aperture ratio is decreased, the screen
becomes darker, resulting in lowered image quality.
In order to prevent a lowering of the aperture ratio due to an
increase in the number of pixels, the formation of microlenses on
one of the surfaces of a liquid crystal display element was
proposed (see Japanese Publication for Unexamined Patent
Applications No. 165621-165624/1985 and 262131/1985). The formation
of a plurality of microlenses corresponding to the respective
pixels enables light which is blocked by the black matrix in a
conventional display element to be converged onto a pixel.
In addition, it is possible to use a microlens as: converging means
in an optical pick up for laser disks, compact disks and
magneto-optical disks; converging means for coupling an optical
fiber with a light emitting element or a light receiving element;
converging means or imaging means for improving the sensitivity of
a one-dimensional image sensor for use in a solid image pickup
element such as a CCD and in a facsimile machine (see Japanese
Publication for Unexamined Patent Applications No. 17620/1979 and
9180/1982); imaging means for forming on a photoreceptor an image
to be printed by a liquid crystal printer or an LED printer (see
Japanese Publication for Unexamined Patent Application No.
44624/1988); and a filter for use in optical information
processing. Thus, microlenses are used together with various
optical elements or optical parts in an optical instrument.
A microlens is manufactured, for example, by the following methods:
ion exchange method (Appl. Optics 21(6), p. 1052 (1982), and
Electron Lett. 17, p. 452 (1981)); swelling method (Suzuki et al.
"New Method for Manufacturing Plastic Microlens", 24th Meeting for
Microoptics); "Technique for monolithic fabrication of microlens
arrays" (Zoran D. Popovic et al., Appl. Optics 27, p. 1281 (1988));
and machining.
A microlens of distributed refractive indexes is obtained by the
ion exchange method. A microlens having semi-spherical refracting
surface or paraboloid of revolution (non-spherical refracting
surface) is obtained by the other methods. If the microlens is
semi-spherical, mass production of the microlens is available by
using a semi-spherical microlens as a master (see the 2P method,
Japanese Publication for Unexamined Patent Application No.
134103/1993).
By bonding such microlenses on a liquid crystal display element,
the effective aperture ratio of the liquid crystal display element
is improved, resulting in increased screen luminance. The effective
aperture ratio means a transmission rate of a liquid crystal
display element without a color filter and a polarizing plate.
However, a liquid crystal display element for use in a projection
television, which shows highly definite images with a pixel pitch
of around several tens .mu.m, has a reduced aperture area. Thus,
there is a limit to improving the effective aperture ratio because
the effective aperture ratio depends on a relationship between the
size of a spot of light converged by the microlens and the area of
the apertures of pixels.
A diameter D of the converged light spot is calculated by
where .theta. is a divergence half angle of incident light and f is
a focal length of the microlens. If the area of the converged light
spot becomes larger than the aperture area of pixels, light which
does not fall on the pixels is not used for displaying images,
thereby limiting the improvement of the effective aperture
ratio.
In order to effectively converge light, the divergence .theta. of
the incident light and the focal length f of the microlens may be
decreased. The divergence .theta. of the incident light becomes
smaller as the light emitting area of a light source in use becomes
smaller and the distance from the light source to the liquid
crystal display element becomes larger. With currently available
techniques for light source, however, it is difficult to achieve an
angle of less than several degrees for obtaining a longer life and
necessary brightness for display. Consequently, there is a need to
reduce the focal length f of the microlens and to locate the focal
point of the microlens in the vicinity of the aperture of the pixel
of the liquid crystal display element.
With the current manufacturing techniques, a liquid crystal display
element including pixels with apertures having a side of around 30
.mu.m and a pixel pitch of 50 .mu.m is manufactured. With a liquid
crystal display element of this size, if the divergence .theta. of
illuminating light is 5.degree., the focal length needs to be set
not larger than 170 .mu.m according to the equation (1) in order to
achieve a converged light spot with a diameter D of 30 .mu.m. On
the other hand, since the convergence of the microlens is
proportional to the area thereof, the highest convergence is
achieved by arranging microlenses at the same pitch as a pixel
pitch P without space, i.e., by setting the microlens diameter to
be equal to the pixel pitch P. In this case, the numerical aperture
NA of the microlens is NA=P/(2.multidot.f)=0.147. With such a high
definition liquid crystal display element in which the pixel pitch
P is several tens .mu.m, the numerical aperture of the microlens
for reducing the size of a converged light spot is preferably set
at least 0.1.
With the structure of the above-mentioned microlens, it is
necessary to sandwich glass of a thickness of around 250 .mu.m
which corresponds to the focal length of 170 .mu.m in the air (a
value obtained by multiplying the refractive index of the glass) so
that the focal point is located on the aperture of the pixel of the
liquid crystal display element. In order to achieve this structure,
a liquid crystal display element may be produced by using a piece
of glass with a thickness of 250 .mu.m as a substrate and bonding
microlenses thereon. However, this method is not suitable for mass
production because such thin glass of a thickness of 250 .mu.m is
difficult to handle.
Then, technique for reducing the focal length of a microlens is
disclosed in Japanese Publication for Unexamined Patent Application
No. 248125/1991. With this technique, cover glass or a cover film
of a thickness corresponding to the focal length is attached to a
surface of the microlens, and thus the microlens is fabricated
within a substrate of a liquid crystal display element. Moreover,
Japanese Publication for Unexamined Patent Application No.
233417/1991 discloses a method for achieving mass production and
improved adhesion of a liquid crystal display element by forming a
lens-like section on a lens substrate by a photosensitive resin
according to the 2P method and attaching cover glass having the
same coefficient of thermal expansion as the microlens to the lens
substrate with a bonding agent having a refractive index different
from that of the lens-like section.
However, with the technique for producing a microlens within a
substrate of a liquid crystal display element, although there is no
need to handle a very thin glass substrate, it is necessary to form
transparent electrodes, an alignment film and a black matrix, if
necessary, on a substrate (i.e., cover glass) after producing a
microlens by attaching the cover glass to the substrate. Thus, this
method may cause other problems, for example, a lowering of
transparency of the liquid crystal display element due to
deterioration of the microlens material and bonding agent, and the
separation of the lens from the cover glass. In short, it is hard
to say that the productivity in mass production is improved.
More specifically, in a conventional structure, transparent
electrodes, an alignment film, a black matrix are formed on a glass
substrate under a high temperature not lower than 150.degree. C.,
generally, around 200.degree. C. Such a heat treatment causes no
trouble in the method in which a microlens is bonded to one of
substrates after bonding these substrates (i.e., after heat
treatment). However, if such a heat treatment is carried out after
fabricating a microlens within a substrate, degradation of
materials and separation of lens may occur as mentioned above
because of the thermal resistance of the microlens material and of
the bonding agent.
In order to avoid such problems, the heating temperature may be
lowered when forming transparent electrodes, an alignment film and
a black matrix on a glass substrate. However, if the heating
temperature is lowered, the adhesion of film and the degree of
orientation of liquid crystal will be lowered. As a result, the
reliability of a liquid crystal display element and of a liquid
crystal projector using the liquid crystal display element are
lowered, thereby degrading the display quality. Thus, such a method
is not suitable.
SUMMARY OF THE INVENTION
In order to solve the problems, the present invention is carried
out and objects of the present invention are to fabricate a
microlens substrate including a microlens having a satisfactory
thermal resistance and a short focal length and to provide a
high-quality highly reliable liquid crystal display element of
improved screen luminance and a high-performance liquid crystal
projector with the use of the microlens substrate.
In order to solve the above problems, a microlens substrate of the
present invention, includes:
a first transparent substrate;
a microlens array or a lenticular lens formed on the first
transparent substrate; and
a second transparent substrate,
wherein the second transparent substrate is bonded to the microlens
array or the lenticular lens with a bonding agent, and
the microlens array or the lenticular lens and the bonding agent
are formed by materials having thermal resistance to high
temperatures not lower than 150.degree. C.
With this structure, since the microlens array or lenticular lens
(hereinafter just referred to as the microlenses) and the bonding
agent are formed by materials having thermal resistance to high
temperatures not lower than 150.degree. C., the microlens substrate
has excellent thermal resistance and various processing is
executable under high temperatures. Moreover, since the microlens
substrate is formed by bonding the second transparent substrate
(for example, cover glass) to the microlenses (for example, made of
a heat-resistant resin) formed on the first transparent substrate
with the bonding agent, the microlens is formed within the
substrate. This structure enables the focal length of the microlens
to become shorter than that of a microlens bonded to a
predetermined substrate by post-processing.
Consequently, it is possible to obtain a microlens substrate which
has excellent thermal resistance, permits various processing under
high temperatures, and achieves a shorter focal length.
Accordingly, for example, a liquid crystal display element, which
is constructed by forming transparent electrodes, an alignment
film, and a black matrix, if necessary, on the microlens substrate
as an opposed substrate and bonding the opposed substrate to an
active matrix substrate, can never cause a lowering of transparency
due to decomposition of bonding agent and the microlens material
and the separation of the microlenses from the second transparent
substrate even after executing thermal processing under high
temperatures not lower than 150.degree. C. for forming the
transparent electrodes, the alignment film and the black matrix. It
is thus possible to obtain a high-quality, reliable liquid crystal
display element with improved screen luminance through the same
processes as in the conventional manufacturing method.
The numerical aperture of the microlens array or the lenticular
lens is preferably set at least 0.1. With the above-mentioned
structure, since the numerical aperture is set not lower than 0.1,
this microlens substrate satisfies such a requirement that,
generally speaking, the numerical aperture of lens is preferably
increased to at least 0.1 in order to converge light into a smaller
spot, described in the prior art section. Thus, if a liquid crystal
display element is constructed using this microlens substrate, the
liquid crystal display element achieves a high definition display
with a pixel pitch of around several tens .mu.m.
It is also preferable to arrange the difference .increment.n in the
refractive indexes between the microlens array or lenticular lens
and the bonding agent of the microlens substrate to be not smaller
than 0.1. In this case, since the difference .increment.n in the
refractive indexes between the microlenses and the bonding agent of
the microlens substrate is not smaller than 0.1, the microlens
substrate also satisfies the above-mentioned requirement. More
specifically, denoting a radius of the microlens, the focal length
and the difference in the refractive indexes between the
microlenses and the bonding agent as R, f and .increment.n,
respectively, the numerical aperture of the lenses is approximated
by R/f. Namely, the requirement to be satisfied is R/f.gtoreq.0.1.
Meanwhile, the relationship among these three variables is given by
R=.increment.n.multidot.f by geometrical optics. Thus, the
above-mentioned requirement is rewritten as
.increment.n.gtoreq.0.1. Hence, for example, a liquid crystal
display element constructed by such a microlens substrate becomes a
high definition display with a pixel pitch of around several tens
.mu.m.
If a liquid crystal display element including a microlens substrate
having the above-mentioned structure is used for a liquid crystal
projector, a high-quality, highly reliable liquid crystal projector
is obtained. More specifically, since the microlens array,
lenticular lens and bonding agent are formed from materials having
resistance to temperatures not lower than 150.degree. C., it is
possible to prevent a heating treatment from causing the
decomposition of the materials of the microlenses and bonding agent
and a lowering of the transparency thereof. Consequently, when an
image on the liquid crystal display element is enlarged and
projected onto the screen, the image on the screen does not have
changes in color nor become darker. Thus, a high-quality image is
projected onto the screen. In this case, it is preferable to
arrange a projection lens for converging light transmitted through
the liquid crystal display element and projecting the light onto a
screen to have a numerical aperture larger than that of the
microlens array or lenticular lens. With this arrangement, the loss
of light in the projection lens is certainly decreased, thereby
displaying significantly bright projected images on the screen.
For a fuller understanding of the nature and advantages of the
invention, reference should be made to the ensuing detailed
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section for explaining a structure of a liquid
crystal display element according to one embodiment of the present
invention.
FIGS. 2(a) to 2(d) are explanatory views for explaining a process
of manufacturing a stamper which is used by the 2P method.
FIGS. 3(a) to 3(d) are explanatory views for explaining a process
of manufacturing a microlens array using the stamper.
FIG. 4 is a cross section of an essential section for explaining a
semi-spherical microlens (having a spherical surface) on a
microlens substrate in the liquid crystal display element.
FIG. 5 is a view explaining an essential structure of a liquid
crystal projector using the liquid crystal display element.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[Embodiment 1]
The following description discusses one embodiment of the present
invention with reference to FIGS. 1 to 2. In this embodiment, a
microlens substrate of the present invention is used as an opposed
substrate in a liquid crystal display element. However, this
embodiment is not intended to limit the use of the microlens
substrate of the present invention. Needless to say, the
microlenses of the present invention are utilized in various fields
described in the prior art section.
A liquid crystal display element according to this embodiment is an
active-matrix liquid crystal display element, and includes a
transparent substrate 7 made of quartz glass as shown in FIG. 1.
Formed on the transparent substrate 7 are pixel electrodes,
switching elements, and buslines, not shown. A liquid crystal layer
6 is sealed in a space between the transparent substrate 7 and an
opposed substrate (i.e., the microlens substrate of the present
invention) 9 facing the transparent substrate 7 by a sealing
material 5.
The opposed substrate 9 is constructed by a transparent substrate
(first transparent substrate) 1 made of quartz glass, a microlens
8, a bonding layer 3 of a bonding agent, and cover glass (second
transparent substrate) 4 made of quarts glass.
The microlens 8 is a so-called microlens array having a plurality
of lens sections 2 which correspond to the respective pixel
electrodes on the transparent substrate 7. In this embodiment, each
of the lens sections 2 of the microlens 8 is shaped into a
semi-spherical convex lens having a spherical surface by the
above-mentioned 2P method.
With the 2P method, a mold called a stamper for the microlens array
is first produced. Then, a large number of microlens arrays are
fabricated using the stamper. This process is simply described
below with reference to FIGS. 2 and 3.
First, the process of producing the stamper is explained with
reference to FIG. 2.
(a) Preparing a substrate 11 and applying an electron beam resist
12 onto the substrate 11.
(b) Softening and shaping the electron beam resist 12, which has
been patterned by the exposure of an electron beam, into a convex
lens for producing a microlens array master 13.
(c) Introducing a stamper material such as nickel on the master 13
by electroforming so as to produce a nickel stamper 14.
(d) Separating the stamper 14 from the master 13. As a result, the
stamper 14 has a concave shape corresponding to the convex shape of
the microlens array. This is used as a mold for the microlens
array.
The process of producing the microlens array with the use of the
stamper 14 is explained below with reference to FIG. 3.
(a) Preparing a transparent substrate 15, and introducing an
ultraviolet sensitive resin (a so-called UV hardening resin) 16 in
the stamper 14.
(b) Sandwiching and pressing the introduced ultraviolet sensitive
resin 16 by the stamper 14 and the transparent substrate 15 so that
the resin 16 spreads over the entire lens surface.
(c) Hardening the ultraviolet sensitive resin 16 by ultraviolet
light passed through the transparent substrate 15.
(d) Separating the transparent substrate 15 and the ultraviolet
sensitive resin 16 after hardened from the stamper 14. The
separated object is a microlens array.
Transparent electrodes, an alignment film and a black matrix, not
shown, are formed on a surface of the cover glass 4 facing the
liquid crystal layer 6. These are formed under high temperatures
not lower than 150.degree. C. after bonding the microlens 8 and the
cover glass 4 to form a microlens substrate. Therefore, the
microlens 8 and the bonding layer 3 need to have thermal resistance
so that they are not decomposed nor deformed and that the
transparency thereof is not lowered even at temperatures higher
than 150.degree. C.
FIG. 4 illustrates an enlarged view of an essential section of the
lens section 2 of the microlens 8 formed on the transparent
substrate 1. In FIG. 4, n1, n2, n3 (=1) represent refractive
indexes of the microlens 8, the bonding agent 3 and the air,
respectively. The difference .increment.n in the refractive indexes
of the resins is defined by
Additionally, in FIG. 4, R is a radius of curvature (i.e., a half
of the length of the aperture of the lens) of the lens section 2,
and f is a focal length of the lens section 2 in the air. As
described above, in order to decrease the diameter of a converged
light spot, it is essential to select a resin having a refractive
index satisfying .increment.n.gtoreq.0.1.
In this embodiment, in order to satisfy the above-mentioned two
conditions, the microlens 8 was formed by a photosensitive resin
"UV-4000" having a refractive index n=1.567 and the bonding layer 3
was formed by a photosensitive resin "UV-1000" having a refractive
index n=1.453. Both UV-4000 and UV-1000 are manufactured by Daikin
Kogyo Co., Ltd.
The thermal decomposition temperatures of these resins are not
lower than 150.degree. C., and thermal decomposition or color
changes were not observed when vacuum depositing the transparent
electrodes and the black matrix under temperatures not lower than
150.degree. C. .increment.n=0.114 is obtained by the equation (2).
The microlens 8 suitable for a liquid crystal display element
having the structure mentioned in this embodiment and a pixel pitch
of 29 .mu.m.times.24 .mu.m was designed based on the value. As a
result, when the lens section 2 had a spherical surface whose
radius of curvature is 18.8 .mu.m, the focal length f in the air
was 165 .mu.m. Since the refractive index of quartz is 1.46, the
thickness of the cover glass 4 becomes 240 .mu.m. In short, this
microlens 8 improves the effective aperture ratio of the liquid
crystal display element.
As described above, in the liquid crystal display element of this
embodiment, the microlens substrate including the microlens 8 and
the bonding agent 3 which are formed by the heat-resistant resins
is used as the opposed substrate 9 in the liquid crystal display
element. Therefore, even if heat is applied to the opposed
substrate 9 when forming the alignment film, the transparent
electrodes and the black matrix, decomposition and deformation of
the materials can never occur. It is thus possible to produce a
liquid crystal display element by carrying out the same processes
under the same manufacturing conditions as the conventional
processes and conditions, and to improve the reliability of the
microlens 8 and of the liquid crystal display element.
Moreover, since the microlens 8 having a large numerical aperture
is attached by the bonding layer 3 having a refractive index
different from that of the microlens 8, it is possible to produce
lens effects even when the lens sections 2 and the bonding layer 3
are in contact with each other. Consequently, the focal length of
the microlens 8 is shortened and the convergence thereof is
increased. It is thus possible to obtain a high-quality highly
reliable liquid crystal display element with improved screen
luminance.
Instead of the heat-resistant resins used in this embodiment, the
materials listed below, which have resistance to high temperatures
not lower than 150.degree. C. may be used for forming the microlens
8. The microlens 8 may be formed by the following photosensitive
resins: "RC-8766" (refractive index n=1.534) from Dainippon Ink
& Chemicals, Inc.; and "MO1" (refractive index n=1.52), "UT20"
(refractive index n=1.51), "HO2" (refractive index n=1.63) and
"HV2" (refractive index n=1.63) from Ardel. The bonding layer 3 may
be formed by the following photosensitive resins: "HNA-101"
(refractive index n=1.37) from Dainippon Ink & Chemicals, Inc.;
and UV-2000 (refractive index n=1.477) and "UV-3000" (refractive
index n=1.498) from Daikin Kogyo Co., Ltd.
In this embodiment, the transparent substrate 1, the cover glass 4,
and the transparent substrate 7 are formed by the same material.
The reason for this is to prevent the separation of the microlens 8
and the respective substrates due to different coefficients of
thermal expansion. Considering productivity, it is desirable to use
ultraviolet sensitive resins rather than thermosetting resins for
the microlens 8 and the bonding layer 3.
[Embodiment 2]
In embodiment of the present invention, a liquid crystal projector
is manufactured using the liquid crystal display element of the
above-mentioned embodiment. The use of the liquid crystal display
element having an increased effective aperture ratio achieves
definite images and a high-quality liquid crystal projector.
The following description discusses in detail a liquid crystal
projector using a liquid crystal display element utilizing the
microlens substrate of Embodiment 1 with reference to FIG. 5.
The liquid crystal projector includes an optical system 25 in FIG.
5. In the optical system 25, light irradiated by a white light
source 17 such as a metal halide lamp is guided to dichroic mirrors
19a and 19b through a UV-IR filter 18. With the dichroic mirrors
19a and 19b, the incident light is separated into three primary
colors: red, green and blue.
For example, the dichroic mirror 19a reflects only the blue light,
and the dichroic mirror 19b reflects only the green light. In this
case, the blue light separated by the dichroic mirror 19a is guided
to a liquid crystal display element 21a through a reflecting mirror
20a. The green light and red light transmitted through the dichroic
mirror 19a fall on the dichroic mirror 19b. The dichroic mirror 19b
reflects only the green light toward a liquid crystal display
element 2lb. The red light is transmitted through the dichroic
mirror 19b and guided to a liquid crystal display element 21c.
Each of the liquid crystal display elements 21a to 21c includes the
microlens substrate explained in Embodiment 1, and displays images
with primary colors based on video signals. The blue light
transmitted through the liquid crystal display element 21a falls on
a dichroic mirror 23a through a field lens 22a. The green light
transmitted through the liquid crystal display element 2lb falls on
the dichroic mirror 23a through a field lens 22b. The red light
transmitted through the liquid crystal display element 21c falls on
a dichroic mirror 23b through a field lens 22c and a reflecting
mirror 20b. The primary color light transmitted through the liquid
crystal display elements 21a to 21c is synthesized by the dichroic
mirrors 23a and 23b, and guided to the projection lens 24. Then,
enlarged images are projected onto a screen, not shown.
In the liquid crystal projector, as the liquid crystal display
element has a smaller size (becomes more definite), a microlens
having a shorter focal distance is provided for each pixel. With
this arrangement, since light which is blocked by the black matrix
in a conventional high-definition liquid crystal display element is
effectively converged onto the aperture of a pixel by the
microlens, a bright display is achieved. More specifically, since
the microlens array, lenticular lens and bonding agent are formed
from materials having resistance to temperatures not lower than
150.degree. C., it is possible to prevent a heating treatment from
causing the decomposition of the materials of the microlenses and
bonding agent and a lowering of the transparency thereof.
Consequently, when an image on the liquid crystal display element
is enlarged and projected onto the screen, the image on the screen
does not have changes in color nor become darker. Thus, a
high-quality image is projected onto the screen.
After the light is converged into a spot by the microlens, it
travels toward the projection lens 24 while being diverged from the
aperture of a pixel at an angle (diverging angle) which is
determined by the numerical aperture of the pixel. In order to
converge the divergent light with a small loss by the projection
lens 24, it is desirable to decrease the focal distance f of the
projection lens 24 and increase the aperture D thereof. It is thus
preferable to set D/2f that is the numerical aperture of the
projection lens 24 larger than the numerical aperture of the
microlens. Therefore, when a projection lens 24 having a numerical
aperture not smaller than 0.1 is used to meet the requirements for
the numerical aperture of the microlens, it is possible to reduce
the loss of light in the projection lens 24, thereby displaying
highly bright projected images on the screen.
In the above explanation, the dichroic mirror 19a reflects only the
blue light, and the dichroic mirror 19b reflects only the green
light. However, the present invention does not necessarily have
this structure. Here, it is only necessary to separate the light
irradiated by the white light source into three primary colors:
red, green and blue.
As described above, a microlens substrate of the present invention
includes: a first transparent substrate; a microlens array or a
lenticular lens (hereinafter referred to as the microlenses) formed
on the first transparent substrate; and a second transparent
substrate, wherein the second transparent substrate is bonded to
the microlenses with a bonding agent, and wherein the microlenses
and the bonding agent are formed by materials having thermal
resistance to high temperatures not lower than 150.degree. C.
Those microlenses have excellent thermal resistance, and permit
various processing under high temperatures. For instance, if a
substrate including the microlenses formed therein is used for one
of substrates constructing a liquid crystal display element, and if
the microlenses are heated to high temperatures in fabricating the
liquid crystal display element, the liquid crystal display element
is fabricated under the same manufacturing conditions as for a
conventional liquid crystal display element without causing
decomposition and deformation of the microlens material and the
bonding agent.
Moreover, since the microlens substrate of the present invention is
fabricated by bonding the second transparent substrate (for
example, cover glass) to the microlenses (for example,
heat-resistant resin) on the first transparent substrate, the
microlenses are formed within the substrate. This structure enables
the focal length of the microlenses to become shorter than that of
a microlenses bonded as separate pieces to a predetermined
substrate by post-processing.
If the microlens substrate having this structure is used for a
liquid crystal display element, a high-quality highly reliable
liquid crystal display element with increased luminance (increased
effective aperture ratio) is achieved. Furthermore, with the use of
such a liquid crystal display element having an increased effective
aperture ratio, highly definite images are obtained and a
high-quality liquid crystal projector is achieved.
The invention being thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *